Apparatus, systems and methods for high efficiency metal particle regeneration

ABSTRACT

A method for generating a metallic particle slurry in a regenerator, the method comprising the steps of: (a) generating metallic particles on a surface of a cathode by applying a forward current for a forward current period; (b) displacing the metallic particles from the surface of the cathode by applying a displacement force for a displacement period; (c) dissolving residual metallic particles by applying a reverse current for a reverse current period; (d) providing a plurality of regenerator cells; and (e) establishing an airlock by isolating aqueous electrolyte between cavities of regenerator cells.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 16/335,771,entitled “APPARATUS, SYSTEMS AND METHODS FOR HIGH EFFICIENCY METALPARTICLE REGENERATION”, filed Mar. 22, 2019, which is incorporatedherein by reference. U.S. patent application Ser. No. 16/335,771 is a371 national phase entry of Patent Cooperation Treaty patent applicationNo. PCT/CA2017/051105 filed Sep. 19, 2017, which claims priority to andthe benefit of U.S. provisional patent application No. 62/399,254 filedSep. 23, 2016. All of the foregoing applications are incorporated byreference herein in their entireties for all purposes.

TECHNICAL FIELD

This invention relates to apparatus, systems and methods for metalparticle regeneration.

BACKGROUND

U.S. Pat. No. 5,228,958 discloses a method of preparing zinc alkalislurry and a method of separating the slurry into dissolved andundissolved phases. Zinc particles are made from the dissolved phase at10 to 600 mAcm⁻² and are deposited onto a cathode unit which must bephysically transferred to separate containers to undergo a zinc removalprocess.

U.S. Pat. No. 6,436,539 further discloses a method of preparingcorrosion resistant dendritic zinc alloy particles at 20 to 200 mA cm².The deposited dendritic zinc alloy is periodically removed from acathode unit known methods in the art. It also discloses that theremoved zinc alloy can be homogenized by methods such as blending.

U.S. Pat. No. 7,166,203 describes a method for making zinc particles forzinc air fuel cells, but the higher current density of 500 to 5000 mAcm⁻² makes for at least an inefficient generation.

Apparatus, systems and methods for improved efficiency in metal particleregeneration are desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views of the basic elements andstructure of a regenerator cell according to an embodiment of theinvention.

FIGS. 1C and 1D are cross-sectional views of the basic elements andstructure of a regenerator cell according to a further embodiment of theinvention.

FIG. 2 is a block diagram of a regenerator in-situ process according toan embodiment of the invention.

FIG. 3A is a cross-sectional view of the regenerator cell according tothe embodiment of the invention shown in FIGS. 1A and 1B in a particledeposition process.

FIG. 3B is a cross-sectional view of the regenerator cell according tothe embodiment of the invention shown in FIGS. 1A and 1B in a particledisplacement process and a particle dissolution process.

FIG. 4A is a cross-sectional view of a regenerator cell according to anembodiment of the invention, in a particle displacement process and aparticle dissolution process wherein a radial arm is attached to aninlet port to achieve localized distribution of electrolyte across thecathode surface.

FIG. 4B is a cross-sectional view (perpendicular to the view of FIG. 4A)of the embodiment shown in FIG. 4A, in a particle displacement processand a particle dissolution process wherein the inlet port is driving therotation of the radial arm.

FIGS. 5A to 5D are front views of radial arms according to embodimentsof the invention.

FIG. 6A is a cross-sectional view of a regenerator cell according to anembodiment of the invention, showing the basic electrical circuitsbetween the anode and the cathode in a particle deposition process.

FIG. 6B is a cross-sectional view of a regenerator cell according to theembodiment shown in FIG. 6A, showing the basic electrical circuitsbetween the anode and the cathode in a particle displacement process anda particle dissolution process.

FIG. 7A is a partial cross-sectional via of a regenerator cell accordingto an embodiment of the invention, showing the offset relationshipbetween the cathode and the anode, wherein the anode is smaller than thecathode according to an offset distance.

FIG. 7B is a partial cross-sectional via of a regenerator cell accordingto an embodiment of the invention, showing a non-porous andnon-conductive coating applied to further prevent an edge deposition.

FIG. 8 is a schematic illustration of the basic elements and structureof a regenerator stack according to an embodiment of the invention,wherein the rotation of the manifold is driven by an external component.

FIG. 9 is a cross-sectional view of the basic elements of a regeneratorstack according to an embodiment of the invention.

FIG. 10A is a cross-sectional view of the basic elements and structureof a regenerator stack according to an embodiment of the invention, witha plurality of cells wherein a shunt current exists.

FIG. 10B is a schematic illustration of the basic elements and structureof the regenerator stack according to an embodiment of the invention,with a plurality of cells wherein the shunt current is eliminated by anair lock mechanism.

FIG. 10C is a schematic illustration of an intermediate tank and of thebasic elements and structure of the regenerator stack with a pluralityof cells according to an embodiment of the invention, wherein the liquidlevel in the regenerator stack is identical to the liquid level of theintermediate tank when electrolyte is static and the system is either atequilibrium or at the particle generation step,

FIG. 10D is a schematic illustration of an intermediate tank and of thebasic elements and structure of the regenerator stack according to anembodiment of the invention, with a plurality of cells where the liquidlevel in the regenerator stack is higher than the liquid level of thesystem tank wherefrom electrolyte is pumped.

FIG. 11 is a block diagram illustrating the basic elements of theregenerator bay according to an embodiment of the invention, wherein theintermediate tank enables the compartmentalization of a plurality ofregenerator stacks at different levels relative to the main system tank.

FIG. 12 is a schematic illustration of the basic elements and structureof the regenerator stack with a plurality of cells according to anembodiment of the invention, wherein the intermediate tank is integratedinto said regenerator stack.

FIG. 13A is a schematic illustration of the basic elements and structureof the regenerator stack with a plurality of cells and an integratedintermediate tank according to an embodiment of the invention, whereinthe liquid level of said regenerator stack is identical to the liquidlevel of said integrated intermediate tank when the electrolyte isstatic and the system is either at equilibrium or at the particlegeneration step

FIG. 13B is a schematic illustration of the basic elements and structureof the said regenerator stack with a plurality of cells and anintegrated intermediate tank according to an embodiment of theinvention, wherein the liquid level of said regenerator stack is higherthan the liquid level of said integrated intermediate tank wherefrom theelectrolyte is pumped

FIG. 14 is a block diagram showing an alternative embodiment ofcompartmentalization whereby a plurality of regenerator stacks may beoperatively connected to construct a particle regeneration subsystem.

FIG. 15 is a schematic illustration of a sample in-line componentaccording to an embodiment of the invention, wherein a fixed featurefacilitates the breakage of pressure of the regenerator stack from thatof the sump tank and allows for discrete operation of said stack.

FIG. 16 is a schematic illustration of the circuit diagram of atwo-stage particle dissolution process according to an embodiment of theinvention, wherein a regenerator unit consists of a group ofodd-numbered cells and a group of even-numbered cells wherein theparticle dissolution process is sequentially performed.

FIGS. 17A to 17D are schematic illustrations of undesirable in-situparticle deposition process during the multi-stage particle dissolutionprocess in a regenerator unit consisting of a group of odd-numberedcells and a group of even-numbered cells.

FIGS. 18A to 18D are schematic illustrations of a multi-stage particledissolution process in a regenerator unit according to an embodiment ofthe invention, consisting of a group of odd-numbered cells and a groupof even-numbered cells wherein the repetition of the undesirable in-situparticle deposition can be eliminated.

FIG. 19 is a schematic illustration of a circuit diagram consisting ofdiscrete power supplies in each individual cell to execute discreteparticle dissolution process according to an embodiment of theinvention.

FIG. 20 is a schematic illustration of the basic elements of aregenerator cell according to an embodiment of the invention, whereinsaid regenerator cell consists of the anode, the cathode, or the bipolarelectrode, and the auxiliary electrode.

FIG. 21A is a schematic illustration of the basic elements and structureof a regenerator stack according to an embodiment of the invention, thestack consisting of an anode, a cathode and a third or auxiliaryelectrode in the area wherein the said auxiliary electrode has nophysical contact with the other two electrodes during the particledeposition process.

FIG. 21B is a schematic illustration of the basic elements and structureof a regenerator stack according to an embodiment of the invention, thestack consisting of an anode, a cathode and an auxiliary electrode inthe area wherein during the particle displacement process and theparticle dissolution process the said auxiliary electrode hasestablished ionic contact with the other two electrodes through theelectrolyte.

DETAILED DESCRIPTION OF THE INVENTION

The invention will describe how a high efficiency metal regeneratorstack may be operated to obtain dendritic metal slurry. According tosome embodiments of the invention, metallic particles of a dendriticmorphology are deposited on a cathode unit at a current density in therange from 50 to 600 mA cm². The regenerator cell or stack thenundergoes an in-situ particle removal process wherein the cathode unitis reconditioned for a subsequent deposition process. With reversepolarity dissolution and/or mechanical displacement of depositedmetallic particles, a uniform distribution of metallic particles isreliably attained and can be easily fluidized. The invention willfurther describe what steps must be taken in order to construct areliable and energy efficient regenerator stack, and a method of makingthe same. Some embodiments provide an air-lock mechanism to allow for areliable and uniform metallic particle deposition across any of thecathodes in a plurality of cathodes in series. Some embodiments providean intermediate tank to decouple the operation of each regenerator stackfrom operations of the fuel storage tank and of other regenerator stackshoused in the same metal particle regeneration system or subsystem.

FIGS. 1A and 1B illustrate the basic elements and structure of aregenerator cell 100 according to an embodiment of the invention. Theregenerator cell 100 includes a cathode 102, an anode 103, and aconnector 101. All elements are situated in a cell housing 400 which maycomprise any individual housing, any mechanical supporting element forelectrodes and subcomponents, or any dividing elements for physicalseparations between individual cells. Housing 400 at least partiallydefines a cavity 405 therein. The cathode 102 and anode 103 aresubstantially immersed in an electrolyte 401. The anode 103 comprises aconductive material, for example and not limited to nickel, that isstable in the electrolyte and promotes oxygen evolution. The cathode 102comprises a conductive material, for example and not limited tomagnesium, that is stable in the electrolyte, exhibits low surfaceroughness, and has low adhesion to the deposited metallic material. Theconnector 101 comprises a conductive material that is in physical andelectrical contact with cathode 102. Part of the connector 101 isextended away from the housing 400 to allow for a separate electricalconnection. In some embodiments, the electrolyte 401 comprises anaqueous alkali hydroxide solution and inorganic additives that promotedendritic particle growth and suppress hydrogen evolution and metallicparticle corrosion. In some embodiments, cathode 102 and anode 103 aresubstantially planar in form.

The regenerator cell 100 is further equipped with an inlet port 404 thatenables the fluidic electrolyte 401 to be introduced into the cellthrough jet-hole 301. Inlet port 404 may be rotated by an externalmechanism (not shown) such that a stream of electrolyte 401 emergingfrom jet-hole 301 may sweep the entire surface of cathode 102. Themetallic particles deposited on cathode 102 are dislodged by this actionand may exit regenerator cell 100 through outlet port 402. Inlet port404 is situated below the normal or static level of electrolyte in thecell that is established by outlet port 402.

FIGS. 1C and 1D are cross-sectional views of the basic elements andstructure of a regenerator cell 100 according to a further embodiment ofthe invention. The regenerator cell 100 includes a cathode 102, an anode103, and a connector 101. All elements are situated in a cell housing400 which may comprise any individual housing, any mechanical supportingelement for electrodes and subcomponents, or any dividing elements forphysical separations between individual cells. The cathode 102 and anode103 are substantially immersed in an electrolyte 401. The anode 103comprises a conductive material, for example and not limited to nickel,that is stable in the electrolyte and promotes oxygen evolution. Thecathode 102 comprises a conductive material, for example and not limitedto magnesium, that is stable in the electrolyte, exhibits low surfaceroughness, and has low adhesion to the deposited metallic material. Theconnector 101 comprises a conductive material that is in physical andelectrical contact with cathode 102. Part of the connector 101 isextended away from the housing 400 to allow for a separate electricalconnection. In some embodiments, the electrolyte 401 comprises anaqueous alkali hydroxide solution and inorganic additives that promotedendritic particle growth and suppress hydrogen evolution and metallicparticle corrosion. In some embodiments, cathode 102 and anode 103 aresubstantially planar in form.

The regenerator cell 100 is further equipped with an inlet port 404 thatenables the fluidic electrolyte 401 to be introduced into the cell.Electrolyte entering inlet port 404 may be directed by the geometry ofcavity 405 such that a stream of electrolyte 401 emerging from inletport 404 may sweep the entire surface of cathode 102. The metallicparticles deposited on cathode 102 are dislodged by this action and mayexit regenerator cell 100 through outlet port 402. Inlet port 404 andoutlet port 402 are substantially located at the same height such thatthe normal or static level of electrolyte in the cell ensures thatcathode 102 and anode 103 both remain immersed in electrolyte when theflow of electrolyte from inlet port 404 is terminated.

FIG. 2 shows an in-situ regenerator process 10 according to anembodiment of the invention wherein metallic particles are sequentiallydeposited, displaced, and dissolved.

In particle deposition step 11, metallic particles of a dendriticmorphology are deposited on cathode 102 through electrolytic action. Inparticle displacement step 12, said metallic particles are dislodgedfrom the surface of cathode 102 through a variety of methods that mayinclude physical interaction with a liquid or a gas, sonication andother similar means. Also in particle displacement step 12, saiddislodged metallic particles are removed from the vicinity of cathode102 by an exchange of electrolyte. In particle dissolution step 13,cathode 102 is returned to its original state by applying a reversecurrent to regenerator cell 100 to re-dissolve any residual particlesthat may remain on the surface of cathode 102 after the completion ofstep 12.

In the embodiment of the particle deposition process shown in FIG. 3A,the regenerator cell 100 uses oxidation of hydroxyl ions in theelectrolyte and reduction of a metal ion as the electrochemical reactioncouple to deposit metallic particles 200 on cathode 102. As shown inFIG. 3B, in the particle displacement process the metallic particles 200are displaced from cathode 102 by the jet stream that is introducedthrough inlet port 404 and jet-hole 301 into the cell cavity 405 andexits through the outlet port 402. In the particle dissolution step thepolarities of the two electrodes 102, 103 are reversed through anexternal circuit for example as illustrated in FIG. 6 . The regeneratorcell 100 uses oxidation of metallic particles and reduction of water asthe electrochemical reaction couple to dissolve residual metallicparticles 200 from cathode 102 into the electrolyte 401.

It will be apparent to those skilled in the art that the regeneratorprocess described in FIGS. 3A/3B and based on the regenerator celldescribed in FIGS. 1A/1B is equally applicable to the regenerator celldescribed in FIGS. 1C/1D.

FIGS. 4A and 4B illustrate a regenerator cell for removing the depositedmetallic particles according to an embodiment of the invention. The cellcomprises an inlet port 404 that is equipped with one or a plurality ofjet-holes 301. Inlet port 404 is capable of being rotated about ahorizontal axis. FIG. 4A illustrates the attachment of a radial arm 302for example to the opening of the jet-hole 301 (shown in FIG. 3 ) toextend the jet stream and redirect the jet stream to a localized area ofthe cathode 102 whereon metallic particles 200 may have been deposited.FIG. 4B is a front view schematic illustration of a regenerator cellcomprising an inlet port 404 with a single or a plurality of jet-holes301 wherein the jet-hole 301 is in fluidic connection with the cavity ofradial arm 302 having a single or a plurality of openings 307.

FIGS. 5A to 5D illustrate non-limiting examples of radial arms 302 a,302 b, 302 c and 302 d having a single or a plurality of openings 307,308. Said radial arms can be mounted on said inlet port and may directthe jet stream to specific areas of cathode 102. The degree and numberof openings affect the level of particle dislodgement within the cavityof the regenerator cell. One example is to arrange openings 307 to beevenly spaced along the radial arm to achieve a substantiallydistributed and pressured jet stream across the surface of the cathodefor particle dislodgement. Another example is to limit the number ofopenings 307 to, for example, one, wherein the resulting pressurized jetstream becomes relatively powerful due to the reduction of pressure dropacross radial arm 302. Yet another example is to have a single enlargedopening or an open channel 308 that increases the pressure drop acrossradial arm 302 and yields a high flow jet stream which covers a greaterarea of the cathode surface.

FIGS. 6A and 6B are schematic illustrations of the electrical circuitconnection around the regenerator cell 100 according to an embodiment ofthe invention. FIG. 6A illustrates the circuit configuration whenmetallic particles are being deposited onto cathode 102 by applying acurrent across cathode 102 and anode 103 in a current density range, forexample, between 50 mA cm⁻² and 600 mA cm⁻². FIG. 6B illustrates thecircuit configuration when the deposition of metallic particles ispaused and wherein a particle dissolution step occurs. The connector 101is connected to for example and not limited to a DC to DC converter 122that is used to drive power across the cell to dissolve the metallicparticles 200 into the electrolyte. A voltage, for example but notlimited to, of less than 1.3 V is applied across a cathode and an anode,wherein the polarity of each electrode has been switched to an anode anda cathode, respectively. It will be apparent to those skilled in the artthat DC to DC converter 122 and main power supply 123 are never appliedto regenerator cell 100 simultaneously.

Electrodeposition generally occurs in the presence of electrolyte andconducting electrodes. If there is a physical interface between theelectrode and the cell housing in the presence of electrolyte, duringparticle deposition said deposition typically occurs inside the edge andalong the wall normal to the plane of the electrode. Such deposition isknown as edge deposition. Since said edge deposition exists in alocation away from any jet stream, the dislocation of depositedparticles becomes inefficient or nonexistent. A successive series ofdeposition processes may substantially enlarge said deposited particles,forming, for example but not limited to, clumps of particles which mayshort-circuit the cell or may plug the inlet or outlet of a stack toimpede flow of electrolyte. Accordingly, said clumps of particles maycontribute to a number of failing mechanisms for an electrolyzer cell orregenerator.

According to an embodiment of the invention, said edge deposition can besignificantly reduced by adjusting the relative geometries of the twoelectrodes. FIG. 7A is a schematic cross-sectional illustration of thebasic elements of an electrolytic cell wherein the length, height ordiameter of the anode 103 is shorter than that of the cathode 102. Bothof the cathode and the anode may extend to the cell housing 400. Aclose-up diagram further illustrates the length-to-gap ratio (s/I)between the anode 103 and the cathode 102 wherein the (s) term definesthe difference in diameter or length between said anode and that of saidcathode or the offset distance, and wherein the (I) term defines theseparation between opposite faces of the anode 103 and the cathode 102.Maintaining said ratio within predetermined ranges can significantlyreduce said edge growth. In some embodiments the length-to-gap ratio(s/l) may range from 1:1 to 1:40.

In some embodiments, said edge deposition may be reduced or eliminatedby applying a non-porous and non-conductive coating on the surface ofthe electrode closer to the mechanical interface between a cathode andcell housing. FIG. 7B illustrates the location of said non-conductivecoating 104 wherein the mechanical interface 403 between the housing 400and the edge of the cathode 102 is coated. In one embodiment, thenon-conductive coating 104 can extend to cover the entire lengthdifference, (s). The two described embodiments can be used separately ortogether to inhibit said edge deposition.

FIG. 8 is a schematic illustration of the basic elements and structureof a regenerator stack 600 according to an embodiment of the invention.Regenerator stack 600 includes a plurality of regenerator cellsaccording to the principles of the invention wherein the cathode 102 ofeach cell and the anode 103 of an adjacent cell are in physical andelectrical contact to form a bipolar electrode 105 and said bipolarelectrode provides electrical connection between adjacent cells. Theelectrolyte level 601 of each cell is maintained by an airlock mechanismdescribed in FIG. 10 . An inlet manifold 300 is provided in fluidcommunication with the inlet port (not shown) of each individualregenerator cell. In some embodiments inlet manifold 300 may be a singlecomponent. In other implementations inlet manifold 300 may be assembledfrom a plurality of inlet ports 404 supplying each individualregenerator cell. Inlet manifold 300 may be rotated by, for example andnot limited to, a magnetic, fluidic or mechanical component or anycombination of these components 305. An outlet manifold 303 is providedin fluid communication with the outlet port (not shown) of eachindividual regenerator cell. In some embodiments outlet manifold 303 maybe a single component. In other implementations outlet manifold 303 maybe assembled from a plurality of outlet ports 404 provided by eachindividual regenerator cell.

FIG. 9 is a schematic illustration of the basic elements of aregenerator stack 600 wherein electrolyte is drawn from a source for aparticle displacement process according to an embodiment of theinvention. The particle displacement process includes a washingmechanism to distribute flow across all regenerator cells. Electrolyteis drawn from, for example but not limited to, a fuel storage tank 800.Said fluid flows through the jet-holes 301 of inlet manifold 300 intoeach regenerator cell as a jet stream to displace metallic particles200. Said fluid then exits through outlet manifold 303 at close toatmospheric pressure.

Regenerator cells according to some embodiments of the invention areopen to atmospheric pressure because it is advantageous that the oxygenis able to escape the regenerator cell at atmospheric pressure to avoidthe need for pumps, valves, compressors and storage tanks that mightotherwise be required. For instance, oxygen gas produced by theregeneration process can be released to atmospheric pressure immediatelywithout the need of a gas-liquid separation process, and/or a dedicatedconduit for oxygen transfer to a gas storage tank. The gas release atatmospheric pressure also avoids gas accumulation and any development ofback-pressure that could impede the flow of the gas and adversely affectthe particle deposition process.

Ionic currents are generated and driven by the cell-to-cell potentialgradient of the stack. When each regenerator cell in a stack shares acommon electrolyte wherein a low resistance path exists, a shunt currentoccurs. “Shunt current” is a term to describe the situation wherein thecurrent chooses a less resistive pathway and may bypass intermediatecells to reach (typically) the end cell wherein significant particledeposition occurs due to the increased current flow. In someembodiments, an air-lock mechanism is introduced to significantly reduceor to eliminate shunt current by creating ionic separation between eachcell.

FIGS. 10A and 10B illustrate the importance of an air-lock mechanismaccording to an embodiment of the invention to prevent said shuntcurrent. When electrical current is fed to the terminal cells of abipolar electrolyzer, ionic current 108 is generated and flows acrosseach cell. Some ionic current, especially from end cells, will flowthrough the electrolyte in, for example, the inlet manifold, the outletmanifold and/or the connecting piping to the cell. Said current flowingin this manner is known as shunt current 109 and is shown in FIG. 10A.Said shunt current leads to a higher deposition at cells on one endversus cells on the other end. As illustrated in FIG. 10B, one way tomitigate said shunt current is to eliminate the pathway for shuntcurrent 109 by lowering the electrolyte level from an upper height 702 a(as shown in FIG. 10A) to a lower height 702 b such that the electrolytein each cell cavity 405 is physically separated by both electrodes 102and/or cell housing 400. Cell housing 400 may consist of any individualhousing, any mechanical supporting element for electrodes andsubcomponents or any dividing elements for physical separations betweenindividual cells. This reducing or eliminating of shunt current is madepossible when the outlet manifold 303 shares the same level as that ofthe height 702 b, i.e., said air-lock mechanism. For instance,pressurized electrolyte is being pumped to said stack which is open toatmospheric pressure, as illustrated in FIG. 10A. When the flow ofelectrolyte is stopped, the electrolyte is allowed to be discharged anddrained through outlet manifold 303. As a result, the electrolyte leveldrops from an upper height 702 a to a lower height 702 b and theair-lock is established, creating ionic separation between each cell andthereby eliminating shunt currents, after which an efficient particledeposition process can commence.

FIG. 10C and FIG. 10D are schematic illustrations of an air-lockmechanism and of the basic elements and structure of the regeneratorstack 600 according to an embodiment of the invention. Regenerator stack600 includes a plurality of bipolar electrodes 105 each comprising of acathode 102 and an anode 103. Bipolar electrodes 105 form a plurality ofregenerator cells wherein each regenerator cell shares the sameelectrolyte level 601 a, 601 b with the tank electrolyte level 501 a,501 b.

FIG. 10C is a schematic illustration of a regenerator stack 600 a and anintermediate tank 500 a which are in fluidic connection and positionedat a physical horizontal level. The stack 600 a, 600 b and theintermediate tank 500 a, 500 b are both open to atmospheric pressure,which is integral to releasing the generated oxygen at pressures closeto atmospheric. In a particle deposition process as illustrated in FIG.10C, the electrolyte level 601 a of the stack 600 a is at the sameheight as the electrolyte level 501 a of an intermediate tank 500 a. Asanother advantage, a separated intermediate tank 500 a for eachseparated stack 600 a allows for the decoupling of pressure from thehydraulic head pressure of the fuel storage tank and enables a physicalcompartmentalization into subdivided bay area 902, which is shown andexplained in FIG. 11 .

FIG. 10D is a schematic illustration of the liquid level in theregenerator 601 b in a particle displacement and dissolution processeswherein the liquid level 601 b of the stack 600 b is higher than theliquid level 501 b of the intermediate tank 500 b wherefrom electrolyteis continuously pumped into the regenerator stack 600 b. After thedisplacement and the dissolution processes, there is no electrolyte flowbetween the stack 600 b and the intermediate tank 500 b of which theliquid level allows to come to equilibrium as illustrated in FIG. 10C.

FIG. 11 is a block diagram illustrating one embodiment ofcompartmentalization. There is no pump shown as it is obvious to aperson skilled in the art that a pump or other pressure generatingdevice is required to transfer electrolyte between different units. Thefuel storage tank 800 contains metallic particles and electrolyte at alevel 801. By drawing electrolyte from the fuel storage tank 800, theintermediate tanks 500 can decouple from the hydraulic head pressure offuel storage tank 800 and supply electrolyte to their respectiveregenerator 600 according to their respective hydraulic head pressure.Subdivided bay area 902 can therefore be equipped with regeneratorstacks and intermediate tanks at different vertical heights. Allmetallic particles along with electrolyte from the subdivided bay area902 may be collected in sump tank 805 and subsequently transferred tofuel storage tank 800.

FIG. 12 is a schematic illustration of the basic elements of aregenerator stack 600 according to an embodiment of the invention. Stack600 is equipped with an integrated intermediate tank 701 whereinelectrolyte is drawn from a source through the inlet port 707. Duringthe particle displacement process wherein a washing mechanism isrequired to distribute flow across all regenerator cells, a pump is usedto draw liquid from the intermediate tank 701 and inject electrolyteinto the compartment 704 onto a paddle of a wheel 705. Said injection ofthe fluid onto each of the paddles drives the rotation of the wheelattached to inlet manifold 300. Said fluid escapes the compartment 704through the cavity of the manifold and through the jet-holes 301 intoeach regenerator cell as a jet stream to displace metallic particles200. Said fluid then returns to the tank 701. In a normal operation,metallic particles are periodically transferred to the fuel storage tank(not shown) through the outlet port 708 of the integrated intermediatetank 701.

FIG. 13A is a schematic illustration of an alternative embodiment of aregenerator stack 600 with an integrated intermediate tank 701. Theintegration of said intermediate tank 701 and regenerator stack 600allows for the elimination of connecting piping and a smaller formfactor while maintaining the advantage of compartmentalizationcapability. Components for driving the rotation of the manifold areomitted from the drawing to simplify the schematic. At the start of theparticle deposition process as illustrated in FIG. 13A, the electrolytelevel 702 a of regenerator stack 600 is at the same height as theelectrolyte level 703 a of the integrated intermediate tank 701.

FIG. 13B is a schematic illustration of the electrolyte level in saidregenerator stack 600 during particle displacement and dissolutionprocesses wherein the electrolyte level 702 b of the regenerator stack600 is higher than the electrolyte level 703 b of said integratedintermediate tank 701 wherefrom electrolyte is continuously pumped intosaid regenerator stack 600. After the displacement and the dissolutionprocesses there is no electrolyte flow between regenerator stack 600 andintermediate tank 701 wherein due to the balancing of hydraulic head,electrolyte levels of regenerator stack 600 and intermediate tank 701will return to equilibrium as illustrated in FIG. 13A.

FIG. 14 is a block diagram showing an alternative embodiment ofcompartmentalization whereby a plurality of regenerator stacks may beoperatively connected to construct a particle regeneration subsystem900. Subsystem 900 is primarily comprised of regenerator stacks 600 a,600 b, 600 c, intermediate tanks 701 a, 701 b, 701 c, sump tank 805 andfuel storage tank 800. Regenerator stacks 600 a, 600 b, 600 c areequipped with integrated intermediate tanks 701 a, 701 b, 701 c therebysubstantially eliminating the requirement for interconnecting conduits.Other arrangements and designs of intermediate tanks may work in thisparticle regeneration subsystem 900. The system is recharged by feedingmetal ion-rich electrolyte from sump tank 805 into intermediate tanks701 a, 701 b, 701 c through electrolyte conduits 806 a, 806 b, 806 c.Electrolyte then flows from intermediate tanks 701 a, 701 b, 701 c intoregenerator stacks 600 a, 600 b, 600 c through, but not limited to,internal paths. In a particle deposition process, energy is applied fromexternal source 901 a, 901 b, 901 c to generate metallic particles of adendritic morphology and release oxygen gas, which accumulates in theconnected intermediate tanks 701 a, 701 b, 701 c and conduit 807 a, 807b, 807 c. The intermediate tanks and sump tank release the generatedoxygen at pressures close to atmospheric. In addition, they allow forthe discrete operation of regenerator stacks 600 a, 600 b, 600 c atdifferent electrolyte levels 810 a, 810 b, 810 c. In a particledislocation process, metal ion-rich electrolyte is fed from sump tank805 into intermediate tanks 701 a, 701 b, 701 c and into regeneratorstacks 600 a, 600 b, 600 c through electrolyte conduits 806 a, 806 b,806 c. After the dislocation process in the regenerator stacks finishesas described in FIG. 3B, the electrolyte-particle slurry is thentransferred from intermediate tanks 701 a, 701 b, 701 c into sump tank805 through electrolyte conduits 807 a, 807 b, 807 c. Any accumulatedoxygen is now transferred to and released from the sump tank 805 to theatmosphere. The electrolyte-particle slurry is then delivered from sumptank 805 to fuel storage tank 800 through electrolyte conduit 808. Thesump tank 805 is recharged with fresh electrolyte through conduit 809.Said sump tank provides an exhaust mechanism 802 whereby said dischargedoxygen is released to the atmosphere at atmospheric pressure. Anotherfunction of said sump tank is to provide a mechanism to separateparticles from discharged electrolytes of regenerator stacks 600 a, 600b, 600 c. Said sump tank has features, for example but not limited to abaffle or a particle settling zone, to enable better separation. In someembodiments sump tank 805 can deliver 100 g/L or more of particles tofuel storage tank 800 and 5 g/L or less of particles back to regeneratorstacks 600 a, 600 b, 600 c.

According to an embodiment of an invention, the regenerator stacks 600a, 600 b, 600 c, may include an internal feature which facilitates boththe upholding of atmospheric pressure and the breakage from upstreampressure. One example of said feature is illustrated in FIG. 15 . Saidfeature is incorporated in an in-line component for example but notlimited to a connecting piping or integrated tank. Said feature consistsof inlet pipe 710, outlet pipe 711, and a relatively smallerinterconnecting pipe 712. During both the particle dislocation processand the particle dissolution process, flowing electrolyte from sump tank805 and conduit 806 is being pumped through inlet pipe 710 andsubsequently reaches inlet manifold 300 for flow distribution within thestack. Due to the upstream pressure, dislocated particles along withpressurized flowing electrolyte exits the regenerator stack throughoutlet manifold 303 and outlet pipe 711 to conduit 807 and sump tank805. When the particle dissolution process finishes, the flow ofelectrolyte terminates. Consequently, the siphoning force resulting fromthe atmospheric pressure and downstream gravity pulls the electrolytefrom both the outlet pipe 711 and the regenerator stack 600, and therebyempties the regenerator stack 600. To preserve the electrolyte in saidstack, the interconnecting pipe 712 partially disrupts said force byallowing the electrolyte of the inlet pipe 710 to be pulledsimultaneously, as shown by the flow 713, such that both portions of theoutlet pipe 711 and inlet pipe 710 are drained first before theregenerator stack 600. The interconnecting pipe 712 thus enables thegeneration of an air-gap separation denoted by electrolyte level 714. Inother words, with no moving component the interconnecting pipe 712allows for the preservation of the stack electrolyte and for thedecoupling of pressure from the sump tank. Said interconnecting pipe isdesigned and sized based on the criteria of, for example, 1) providingsurface tension less than said siphon force such that flow from inletpipe 710 can be pulled by said force and 2) limiting flow from goingdirectly from inlet pipe 710 to outlet pipe 711 and thus bypassing theregenerator stack 600.

FIG. 16 is a circuit diagram illustrating the circuit scheme of aparticle dissolution process according to an embodiment of the inventionwherein a plurality of cells is divided into, for example but notlimited to, two groups. The first group consists of odd-numbered cellsconnected to circuit A. The second group consists of even-numbered cellsconnected to circuit B. Cells in both groups are in respective parallelcircuits. Said circuits are established by connecting each connector 101in FIG. 1 (not shown) within each regenerator cell to its respectivecircuit group. The inventors have determined that the particledissolution process cannot be executed across the entire stack at oncebecause this may create an imbalance of metal dissolution efficiency,leading to a discrepancy in the initial condition of each cathode ofsaid regenerator cell prior to the next particle deposition process.Said discrepancy may fail the system over time.

In one embodiment as described in FIGS. 17A to 17D, after the particledeposition process wherein metallic particles 200 are deposited on thecathode 102 as illustrated in FIG. 17A, the particle displacementprocess begins followed by the particle dissolution process. Theseprocesses operations are previously shown in FIG. 2 . Said particledissolution process can be a multi-stage process wherein at the firststage (FIG. 17B), a voltage is applied across each odd-numbered cell andthe metallic particles in the first group of cells dissolve while thesecond group of cells serves as electrical insulation cells. If there isa prolonged particle dissolution process due to the previous depositionunder undesirable conditions in any one of the cells, a small amount ofanodic particles 202 may be deposited on the anode of the same cell atthe completion of the first stage of the dissolution process. After,circuit A is disconnected and subsequently the first group of cellsserves as electrical insulation cells while circuit B applies a voltageacross all even-numbered cells to dissolve their respective metallicparticles as shown in FIG. 17C. Because of the electrically conductivenature of the bipolar electrodes, the insulating cell may have apotential gradient that may lead to a re-deposition of particles 202from one electrode of the odd-numbered cell to the opposite electrode ofthe same odd-numbered cell, and form a small amount of redepositedparticles 203. This embodiment of circuit scheme offers the advantage ofquicker process time as a result of the dissolution process beingperformed in two or more groups of cells instead of in each individualcell.

To further describe, said circuit scheme may have a disadvantage ofpromoting a metal “shuttling” effect, defined as metallic particlesbeing deposited back and forth between the anode 103 and the cathode 102in the consecutive steps consisting of the two- or multi-stage particledissolution process and the particle deposition process. Said shuttlingeffect is especially of concern when the particle displacement processmay become less efficient and an excess amount of metallic particles mayremain on the cathode 102. In the subsequent two-stage particledissolution process wherein polarities of electrodes are reversed, someof the metallic particles in odd-numbered cells (group A in FIGS. 17A-D)are dissolved into the electrolyte while the remainder is deposited ontoa reversed-polarity anode (or, now, cathode) side of the bipolarelectrode, at a much lower current density which may promote plating.Due to the bipolar configuration said reversed-polarity anode is in thesame electrical circuit of the adjacent even-numbered cell, asillustrated by anodic particles 202 in FIG. 17B.

As shown in FIG. 17C when the second stage of the particle dissolutionprocess commences, due to the simultaneous polarization of theeven-numbered cells, particles 202 previously deposited under the firststage may be re-deposited or re-plated (at a lower current density) backto the odd-numbered cells consisting of a reversed-polarity cathode (or,now, anode), as redeposited particles 203. As a result there is alwaysan unaccountable amount of metallic particles 202, 203 remaining on boththe cathode 102 and the anode 103 of the bipolar electrode. Thistwo-stage dissolution step forms a deposition on the anode of theeven-numbered cells and redeposits particles onto cathodes of theodd-numbered cells.

At the anode side of the bipolar electrode 103 the subsequent particledeposition step fully oxidizes any previously deposited anodic particles202 and will not be of concern. On the other hand at the cathode 102,metallic particles are deposited on top of said redeposited particles203 in the next particle deposition process as illustrated in FIG. 17D,forming deteriorated particles 204. Said deteriorated particles 204 havedifferent morphology than that of original metallic particles 200 andmay require more energy to dislocate and dissolve in both thedislocation step and dissolution steps. In addition, as the regenerationprocess continues according to the two-step dissolution process, saiddeteriorated particles 204 may shuttle within a particular cell over theentire operating period, worsening the condition of said cell as itrequires an increasing amount of energy to complete the particledissolution process. Over a number of operating cycles this accumulationof particles may ultimately fail the operation. Said sequence ofoperation can be expressed as GAB-GAB, where A and B are the circuitgroups shown in FIG. 17B and FIG. 17D, respectively, and G denotes aparticle generation step shown in FIG. 17A and FIG. 17D.

To prevent said shuttling effect, an alternative arrangement of the formGAB-GBA as opposed to GAB-GAB may be adopted. Said GBA arrangementeliminates the accumulation of shuttled metallic particles 202, 203within one or more cells by altering the sequence of dissolution stepsand by completely dissolving deteriorated metallic particles 204,particles of different morphology, in the dissolution step. FIGS.18A-18D show the sequence of operations described as GAB-GB A. After theend of the dissolution step for group B (FIG. 17C) and after the nextparticle deposition step (FIG. 18A) that forms both dendritic metallicparticles 200 and deteriorated particles 204, the dissolution step forgroup B is carried out first (FIG. 18B). As such, dendritic metallicparticles 200 are first deposited onto the anode. Next, the dissolutionstep for group A proceeds, wherein deteriorated particles 204 in cell 3and cell 5 are deposited onto the anode of each respective cell, asshown in FIG. 18C. Said arrangement therefore forms deposition on theanode of the odd-numbered cells and redeposit particles onto cathodes ofthe even-numbered cells.

As yet another alternative embodiment, FIG. 19 is a schematicillustration of the circuit arrangement consisting of discrete powersupply 125 connecting to each of a plurality of regenerator cells. Saidpower supply is disconnected from the main power supply 123 for theparticle deposition process. Said arrangement can mitigate the negativeeffect of particle shuttling by performing the particle dissolutionprocess sequentially in each individual cell.

It will be obvious to those skilled in the art that the cells of aregeneration unit can be divided into two or more groups consisting of,e.g., A, B, C, D, E etc., and the sequence of particle dissolutionarrangements can be in any combination of these groups, for example butnot limited to, GABC-GCBA or GABCD-GABCD, in order to achieve theelimination of the particle shuttling effect. Further, it will beapparent to those skilled in the art that the arrangements shown in FIG.16 -FIG. 19 are not exhaustive and that alternative arrangements andcombinations thereof are available and are encompassed by the invention.

FIG. 20 is a schematic illustration of the basic elements and structureof a regenerator stack 600 according to an embodiment of the inventionfurther comprising an auxiliary electrode 106 in the cell cavity whereinthe position of the auxiliary electrode 106 is, for example and notlimited to, directly above the anode 103, the cathode 102, and thebipolar electrode 105, and wherein said auxiliary electrode 106 is notin physical contact with the cathode 102, the anode 103 or a pluralityof bipolar electrodes 105. Said auxiliary electrode is implemented tomitigate said particle shuttling effect and to maintain the advantage ofa simultaneous particle dissolution process in each cell. Said auxiliaryelectrode 106 is made of conducting materials, for example but notlimited to stainless steel, that has high hydrogen evolution potentialto stimulate a fast self-cleaning mechanism wherein any depositedparticles on its surface are galvanically corroded in the electrolyte.In one embodiment the metallic particles are zinc particles and thegalvanic corrosion proceeds according to the following equations:Zn_((s))→*Zn²⁺+2e ⁻H₂O₍₁₎+2e ⁻→H_(2(g))+2OH⁻

FIG. 21A illustrates the electrical circuit and the electrolyte level601 of the regenerator cell in a particle deposition process wherein theelectrolyte level is always below the auxiliary electrode 106 due tosaid air-lock mechanism (see FIG. 11 ). Said auxiliary electrode isconnected to a separate circuit independent from the main circuit.

FIG. 21B illustrates the electrical circuit and the electrolyte level601 of the regenerator cell according to an embodiment of the inventionin both the particle displacement and dissolution processes according toan embodiment of the invention wherein the auxiliary electrode 106 isimmersed in the electrolyte once there is an establishment ofelectrolyte flow (illustrated as arrows). Such immersion allows for theestablishment of an ionic contact between the auxiliary electrode and asingle or a plurality of cathodes 102 wherein a metal dissolutionprocess may be attained. Under a metal dissolution process wherein thepolarity of the electrode is reversed, the cathode of each regeneratorcell becomes the anode. Connecting to a separate circuit, said auxiliaryelectrode then acts as the cathode for every regenerator cell in thestack. This configuration allows for a simultaneous metal dissolutionand in the case wherein a shuttling effect occurs, the metal depositionwill occur on said auxiliary electrode instead of on the originalcathodes 102 as previously discussed.

This application is intended to cover any variations, uses, oradaptations of the invention using its general principles. Further, thisapplication is intended to cover such departures from the presentdisclosure as come within known or customary practice in the art towhich this invention pertains and which fall within the limits of theappended claims. Accordingly, the scope of the claims should not belimited by the preferred embodiments set forth in the description, butshould be given the broadest interpretation consistent with thedescription as a whole.

What is claimed is:
 1. A method for generating a metallic particleslurry in a regenerator, the method comprising the steps of: (a)generating metallic particles on a surface of a cathode by applying aforward current for a forward current period; (b) displacing themetallic particles from the surface of the cathode by applying adisplacement force for a displacement period; and (c) dissolvingresidual metallic particles by applying a reverse current for a reversecurrent period, the method further comprising the steps of: providing aplurality of regenerator cells; and establishing an airlock by isolatingaqueous electrolyte between cavities of the regenerator cells, whereinthe cathode of one regenerator cell is in physical contact with, andelectrically connected to, the anode of an adjacent regenerator cell toprovide a bipolar electrode.
 2. The method according to claim 1,wherein: a density of the forward current ranges from 50 mA cm⁻² to 600mA cm⁻²; the forward current period ranges from 60 s to 180 s; theforward current is achieved by applying a forward voltage; the forwardvoltage being relative to a molarity of potassium zincate within theaqueous electrolyte ranges from 1:0.3 to 1:2; or a size of the metallicparticles is in a range from 25 μm to 200 μm.
 3. The method according toclaim 1, wherein step (b) comprises: flowing liquid across the surfaceof the cathode; and/or vibrating the surface of the cathode; and/orfluidizing with one or more of a liquid phase, a gas phase or a solidphase.
 4. The method according to claim 1, wherein step (c) furthercomprises reversing the polarities of an anode and the cathode in anyone of the regenerator cells or in a group of the regenerator cells, orwherein electrical connectivity of the regenerator cells during step (a)differs from the electrical connectivity of the regenerator cells duringstep (c).
 5. The method according to claim 1, wherein the metallicparticles are zinc particles having a dendritic morphology.
 6. Themethod according to claim 1, wherein the aqueous electrolyte used insteps (a) to (c) comprises a solution formed with at least one chemicalselected from the group consisting of potassium hydroxide, lithiumhydroxide, sodium hydroxide, calcium hydroxide and aluminum hydroxide.7. The method according to claim 6, wherein the aqueous electrolytefurther comprises at least one additive.
 8. The method according toclaim 1, further comprising the step of providing an intermediate tankand positioning a plurality of the regenerator cells relative to theintermediate tank whereby a fluid level of each of the regenerator cellsis maintained at the fluid level of the intermediate tank wherefrom theelectrolyte is drawn.
 9. The method according to claim 7, wherein the atleast one additive is selected from a group consisting of sodiumsilicate, phosphates, sulfates, nitrates, nitrides, sulfides,phosphides, pyrophosphates, crown ethers, polyethylene oxide, and oxidesand hydroxides of indium, bismuth, lead, mercury, and cadmium.